The present invention relates generally to bill identifying devices for use in automatic bending machines, money changing machines, game machines and the like, and more particularly to a paper-like piece identifying method and device for validating (i.e., testing authenticity of) a variety of paper-like pieces, such as bills (bank notes), checks, credit slips, tickets and securities, having distinctive designs or patterns (drawings, characters, etc.) borne on their surfaces as by printing.
Bill identifying or validating devices are known from, for example, Japanese Patent Publication Nos. SHO-63-26918 and SHO-64-5354, which are designed to acquire sample data or detected data by use of sensors to identify types and densities of colors on various regions of a bill as well as magnetic powder contained in the bill in synchronism with transport of the bill and then compare the thus-acquired detected data to a known standard pattern to thereby determine the authenticity or genuineness of the bill. In these known bill identifying devices, an xe2x80x9cauthentic billxe2x80x9d signal for a given denomination is issued only when all the data sampled from individual positions of the bill fall within an allowable tolerance from the known standard pattern for the denomination. Reliability of the thus-identified denomination and authenticity depends only on an evaluated difference between values of the detected data for each of the positions and the standard pattern data. Thus, in order for the bill identifying devices to reliably exclude false bills, it is necessary to set a considerably narrow tolerance as the determination standard; however, too-narrow tolerances could result in the problem that an authentic bill is erroneously determined to be xe2x80x9cfalsexe2x80x9d even when values of detected data for the individual positions have been shifted uniformly by presence of a large stain on the virtually whole surface of the bill.
Further, in the case of bills, such as U.S. dollar bills, having closely similar or approximate printed designs among various denominations, the tolerances for the different denominations would often overlap, which would therefore prevent accurate identification of the bills.
Japanese Patent Publication No. SHO-58-9990 proposes an improved bill identifying device, which is designed to compare detected data for the individual positions to a standard pattern after modifying or adjusting the detected data by use of an average of the data, in order to appropriately deal with undesirable variations in detected data due to stains and aging of a bill and drift of detected data values due to ambient temperature variations. But, the proposed bill identifying device would also erroneously determine and reject an authentic bill as false when the bill has a partial stain thereon presenting a partial detected data variation. Further, Japanese Patent Laid-open Publication No. HEI-2-148383 proposes another improved bill identifying device which prestores relations between standard data and frequency distribution data for each denomination and makes the bill identification on the basis of the fuzzy logic. But, the proposed bill identifying device can not appropriately deal with stains and aging of bills, sensors, etc., because, even when there has occurred a variation in detected data themselves, no specific adjustment is made at all to retain their correspondence with the frequency distribution data.
Because a multiplicity of detected data are generally necessary for accurate identification of denomination and authenticity of a bill, it has been conventional to use optical and magnetic sensors in combination, which, however, would require separate determination circuits for the optical sensors and magnetic sensors, thereby making the overall structure of the device very complex.
Other bill identifying techniques pertinent to the present invention are known from Japanese Patent Laid-open Publications Nos. HEI-3-292589 and HEI-4-102187.
According to the approach disclosed in the HEI-3-292589 publication, sensor-detected data are averaged for subsequent normalization of the data, a ratio of the average value of the sensor-detected data to a predetermined standard average value is determined as an adjustment coefficient, and then the data normalization is effected by multiplying the sensor-detected data by the determined ratio. However, the data normalization employed here is a very simple one and hence would be adversely influenced by various error factors such as stains on individual sensors employed, different operating characteristics and assemblage errors of the sensors and stains on individual bills to be tested.
According to the approach disclosed in the HEI-4-102187 publication, each bill to be tested is divided into a plurality of regions or blocks, a difference is calculated between an average value of detected data for each of the blocks and standard average value data for that block, and the thus-calculated differences for the individual blocks are summed. The sums of such differences are calculated for all denominations, and then one of the denominations for which the calculated sum is the smallest is determined as the denomination of the tested bill. However, because the differences are calculated from an average of absolute values of the detected data, this approach would present the drawback that identification accuracy tends to be poor because bills to be tested have different types and degrees of stains and the like.
It is therefore an object Of the present invention to provide a paper-like piece identifying method and device capable of validating a paper-like piece with increased accuracy by minimizing determination errors that would be caused by detected data variations due to aging of and partial stains on a paper-like piece and by eliminating adverse influences of determination errors due to unique errors and aging of bill-characteristic detecting sensors.
It is another object of the present invention to provide a paper-like piece identifying method and device which achieve appropriate normalization of sample data detected via characteristic-detecting sensors, by performing accurate data adjustment based on extraction of printed design characteristics from the sample data.
It is still another object of the present invention to provide a paper-like piece identifying method and device which achieve accurate validation of a paper-like piece in consideration of uniqueness of the paper-like piece, using statistical totalization of sample data.
It is still another object of the present invention to provide a paper-like piece identifying method and device which can perform validation of paper-like pieces as accurately as possible even when the paper-like pieces are closely similar in design borne thereon.
It is still another object of the present invention to provide a paper-like piece identifying method and device which can perform high-accuracy validation of a paper-like piece only with an optical sensor, without using a magnetic sensor.
According to a first aspect of the present invention, there is provided an paper-like piece identifying method which comprises: a first step of detecting characteristics of a particular paper-like piece to be identified by use of a sensor, to provide detected data for a plurality of predetermined positions on the paper-like piece; a second step of converting the detected data for each of the predetermined positions into relative value data to a predetermined value; a third step of normalizing the relative value data by use of a predetermined normalization parameter, to thereby provide adjusted sample data for each of the predetermined positions; and a fourth step of statistically evaluating the adjusted sample data for each of the predetermined positions by use of a standard average and standard deviation previously set for each of the predetermined positions, to thereby identify the paper-like piece.
By converting the detected data from the sensor into relative value data, it is possible to provide data representative of an extraction of characteristic printed designs on the surface of a paper-like piece (i.e., data corresponding to xe2x80x9cvariation pattern data Dp(I)xe2x80x9d in the later-described preferred embodiment). Further, normalizing the relative value data in the above-mentioned third step provides adjusted sample data (i.e., data corresponding to xe2x80x9cCDATA(I)xe2x80x9d Dp(I) in the later-described preferred embodiment). Such normalization of the relative value data achieves an appropriate data normalization taking into account an unique error of the sensor used and uniqueness of each paper-like piece (such as a stain or wrinkle on whole or part of the paper-like piece). In the above-mentioned fourth step, the adjusted sample data for each of the positions is statistically evaluated using a standard average (parameter corresponding to a xe2x80x9cscan position standard average HMXADR(I) in the later-described preferred embodimentxe2x80x9d) and standard deviation (parameter corresponding to a xe2x80x9cscan position standard deviation HMSADR(I) in the later-described preferred embodimentxe2x80x9d). Such a statistical evaluation significantly enhances the identification accuracy and hence would be useful, in particular, when used for identification of bills, such as U.S. dollar bills, having relatively similar printed design patterns among different denominations.
In a preferred implementation, the above-mentioned second step may include a step of selecting, as the predetermined value, a minimum or maximum value of the detected data for the individual predetermined positions, and the detected data for each of the predetermined positions may be converted into relative value data to the selected minimum or maximum value.
Further, the above-mentioned third step may include: a step of calculating an average value of the relative value data for the predetermined positions; a step of using, as the normalization parameter, a predetermined relative standard average relating to the average value of the relative value data, to calculate a ratio of the average value to the relative standard average as an adjustment coefficient; and a step of executing arithmetic operations for adjusting the relative value data for each of the predetermined positions to thereby provide the adjusted sample data for each of the predetermined positions.
High-accuracy normalization is achieved by thus converting the detected data from the sensor into relative value data to a minimum or maximum value of the detected data and executing arithmetic operations for adjusting, i.e., normalizing the relative value data using, as an adjustment coefficient, a ratio of the average value of the relative value data to a predetermined relative standard average.
In addition, the above-mentioned fourth step may include: a step of, for each of the predetermined positions, executing an arithmetic operation for dividing a difference between the adjusted sample data and the standard average by the standard deviation, to thereby convert the adjusted sample data into a normalized distance value; and a step of evaluating the normalized distance value for each of the predetermined positions in accordance with a predetermined determination standard. With the arrangement, sample data for each of the predetermined positions on the paper-like piece is normalized or standardized in the form of a distance value based on the standard average and standard deviation, which serves to facilitate determination operations on the paper-like piece and also increase the identification accuracy.
The term xe2x80x9cdistance valuexe2x80x9d as used in this specification is chosen only for convenience of description and can not be said to be an established or accepted term in the field of statistics. Here, the term xe2x80x9cdistance valuexe2x80x9d is used to only indicate, in a specific numerical value, how far given sample data differs or deviates from the standard average in terms of a multiple of the standard deviation. Therefore, the term xe2x80x9cdistance valuexe2x80x9d may be replaced by a xe2x80x9cstandardization variablexe2x80x9d as commonly used in the field of statistics. Thus, the distance value of the adjusted sample data based on the sensor output represents, in normalized or standardized form, a distance of the sample data from the standard average (corresponding to the xe2x80x9cscan position standard average HMXADR(I)xe2x80x9d in the later-described preferred embodiment) for each of the predetermined positions on the paper-like piece.
Accordingly, the distance value represents, in normalized form, degree of approximation to the standard average, and a smaller distance value represents a greater approximation to the standard average. Thus, the paper-like piece to be identified can be evaluated appropriately by comparing the distance value to a predetermined determination standard or criterion value (corresponding to a xe2x80x9cscan position determination magnification PMSTxe2x80x9d in the later-described preferred embodiment). Namely, the predetermined determination standard value represents an upper limit of the distance value range defining an acceptable authentic paper-like piece, and if the distance value of the paper-like piece is greater than the determination standard value, the piece will be identified to be non-authentic or false and rejected. Because the distance value is a normalized value, a same or common determination standard value can be applied to distance values for all scan positions of a single sensor. As a consequence, it is possible to considerably simplify creation and storage format of determination standard data. Ultimate standard to be used for finally accepting the paper-like piece as authentic or rejecting it as false may be set optionally. Each paper-like piece may be determined to be authentic if the distance values for all the scan positions of a sensor satisfies a predetermined determination standard and may be determined to be false otherwise, although any other suitable alternative can be applied. Because the determination standard comprises a single value, it can be readily adjusted, which would permit easy adjustment of identifying sensitivity. As a result, the present invention achieves greatly-facilitated adjustment of sensitivity for identifying paper-like pieces.
Introducing the concept of xe2x80x9ctotalized distance valuexe2x80x9d as a parameter for the paper-like piece identification should be very advantageous. The totalized distance value (corresponding to a value xe2x80x9cTODxe2x80x9d in the later-described preferred embodiment) can be calculated by summing normalized distance values for the individual positions. The paper-like piece can be validated by statistically evaluating the totalized distance value by use of previously-set statistical standard data. An example of such statistical standard data may be acquired by: evaluating a totalized distance value standard average (corresponding to an average xe2x80x9cRTXXXxe2x80x9d in the later-described preferred embodiment) and totalized distance value standard deviation (corresponding to a deviation xe2x80x9cRTSIGxe2x80x9d in the later-described preferred embodiment) on the basis of a totalized distance value obtained from a multiplicity of sample paper-like piece; evaluating a limitary value of standardization variable therein by simulation; and then creating a totalized distance value determination standard value (corresponding to a xe2x80x9ctotalized distance value determination magnification TMSTxe2x80x9d in the later-described preferred embodiment). Use of the thus-acquired single totalized distance value for the paper-like identification is very useful for increased identification accuracy. For example, when there has been made a primary judgement that a given paper-like piece corresponds to (i.e., falls in known characteristics) two or more sorts (denominations), one of the sorts (denominations) for which the piece enjoys highest evaluation can be selected by use of the totalized distance value, and thus the totalized distance value can be advantageously used to identify only one actual sort (denomination) of the paper-like piece.
For example, in identification of bills, such as U.S. dollar bills, having relatively similar printed design patterns among different denominations, more reliable identification among the different denominations would be achieved by employing a more stringent determination standard; however, in such a case, it is possible that even authentic bills are often erroneously rejected as not satisfying the stringent determination standard due to aging of and stains on the bills. Further, it has been conventional to use a magnetic sensor, in combination with an optical sensor, to identify respective denominations of bills on the basis of a difference in magnetic content in the printing ink used, which, however, would considerably increase production costs because of the additional provision of the magnetic sensor.
In view of the above-discussed inconvenience encountered by the conventional approach, the present invention is based on an optional design employing a not-so-stringent determination standard or employing only an optical sensor rather than a combination of optical and magnetic sensors, and is characterized by allowing a situation that the primary determination judges a given paper-like piece as corresponding to two or more sorts in an overlapping manner and executing a predetermined secondary determination after such a primary determination to thereby even more increase the identification accuracy.
The present invention can significantly increase the identification efficiency by carrying out the identification by reference to a previously arranged table that stores therein information indicative of a plurality of sorts of paper-like piece approximate to each other in characteristics presented by the sensor detected data.
When the paper-like piece has been judged as corresponding to two or more sorts in an overlapping manner, the secondary determination may be effected in a mode where one of the sorts for which the piece enjoys highest evaluation is selected as the sort of the piece, or alternatively in such a mode where the paper-like piece is determined as false and rejected. Which of the modes should be employed may be set for each combination of predetermined approximate sorts.
Further, in view of the fact that dexterously-made false bills of some large denomination are often encountered, the inventor also proposes a novel solution to eliminate such dexterously-made false bills. Namely, according to the present invention, determination standard data for dexterously-made false paper-like pieces as well as determination standard data for authentic paper-like pieces are previously arranged and stored in memory or the like. When a particular paper-like piece has been determined as satisfying the determination standard data for false paper-like pieces in addition to the determination standard data authentic paper-like pieces, the particular paper-like piece is determined to be false and rejected. This way, the present invention can eliminate such dexterously-made false bills in an appropriate and reliable manner.
The present invention can be arranged and practiced as a paper-like piece identifying device as well as a paper-like piece identifying method. Further, where the present invention is implemented using a computer, it can be practiced as a recording medium containing a paper-like piece identifying program run by the computer.